﻿using System;
using System.Collections.Generic;
using System.Text;

namespace FySystem.Secure
{
    public class CRC
    {
        private const byte polynomialCode_H = 0xA0;
        private const byte polynomialCode_L = 0x01;

        public static ushort[] CRC16Table = {
           0x0, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
           0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
           0x1231, 0x210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
           0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
           0x2462, 0x3443, 0x420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
           0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
           0x3653, 0x2672, 0x1611, 0x630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
           0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
           0x48C4, 0x58E5, 0x6886, 0x78A7, 0x840, 0x1861, 0x2802, 0x3823,
           0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
           0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0xA50, 0x3A33, 0x2A12,
           0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
           0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0xC60, 0x1C41,
           0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
           0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0xE70,
           0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
           0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
           0x1080, 0xA1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
           0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
           0x2B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
           0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
           0x34E2, 0x24C3, 0x14A0, 0x481, 0x7466, 0x6447, 0x5424, 0x4405,
           0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
           0x26D3, 0x36F2, 0x691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
           0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
           0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x8E1, 0x3882, 0x28A3,
           0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
           0x4A75, 0x5A54, 0x6A37, 0x7A16, 0xAF1, 0x1AD0, 0x2AB3, 0x3A92,
           0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
           0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0xCC1,
           0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
           0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0xED1, 0x1EF0
            };

        public static int CRC16(Byte[] dat, int offset, int count)
        {
            int crc = 0;
            Byte crctemp;
            int i = 0;
            while (count > 0)
            {
                count -= 1;
                crctemp = Convert.ToByte(crc >> 8);
                crc = (crc << 8) & 0xFFFF;
                crc = (CRC16Table[crctemp ^ dat[offset + i]] ^ crc) & 0xFFFF;
                i += 1;
            }
            return crc;
        }

        public static int CRC16(List<byte> dat, int offset, int count)
        {
            int crc = 0;
            Byte crctemp;
            int i = 0;
            while (count > 0)
            {
                count -= 1;
                crctemp = Convert.ToByte(crc >> 8);
                crc = (crc << 8) & 0xFFFF;
                crc = (CRC16Table[crctemp ^ dat[offset + i]] ^ crc) & 0xFFFF;
                i += 1;
            }
            return crc;
        }

        public static int CRC16(Span<byte> span)
        {
            int crc = 0;
            Byte crctemp;
            for(int i=0;i<span.Length;i++)
            {
                crctemp = Convert.ToByte(crc >> 8);
                crc = (crc << 8) & 0xFFFF;
                crc = (CRC16Table[crctemp ^ span[i]] ^ crc) & 0xFFFF;
            }
            return crc;
        }

        /// <summary>
        /// Modbus的CRC16
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static byte[] ModbusCrc16(byte[] bytes)
        {
            return ModbusCrc16(bytes, 0, bytes.Length);
        }

        /// <summary>
        /// Modbus的CRC16
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static byte[] ModbusCrc16(byte[] bytes, int offset, int length)
        {
            byte crcRegister_H = 0xFF, crcRegister_L = 0xFF;// 预置一个值为 0xFFFF 的 16 位寄存器

            //byte polynomialCode_H = 0xA0, polynomialCode_L = 0x01;// 多项式码 0xA001

            for (int i = offset; i < offset+length; i++)
            {
                crcRegister_L = (byte)(crcRegister_L ^ bytes[i]);

                for (int j = 0; j < 8; j++)
                {
                    byte tempCRC_H = crcRegister_H;
                    byte tempCRC_L = crcRegister_L;

                    crcRegister_H = (byte)(crcRegister_H >> 1);
                    crcRegister_L = (byte)(crcRegister_L >> 1);
                    // 高位右移前最后 1 位应该是低位右移后的第 1 位：如果高位最后一位为 1 则低位右移后前面补 1
                    if ((tempCRC_H & 0x01) == 0x01)
                    {
                        crcRegister_L = (byte)(crcRegister_L | 0x80);
                    }

                    if ((tempCRC_L & 0x01) == 0x01)
                    {
                        crcRegister_H = (byte)(crcRegister_H ^ polynomialCode_H);
                        crcRegister_L = (byte)(crcRegister_L ^ polynomialCode_L);
                    }
                }
            }

            return new byte[] { crcRegister_L, crcRegister_H };
        }

        /// <summary>
        /// Modbus的CRC16
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static byte[] ModbusCrc16(Span<byte> bytes)
        {
            byte crcRegister_H = 0xFF, crcRegister_L = 0xFF;// 预置一个值为 0xFFFF 的 16 位寄存器

            //byte polynomialCode_H = 0xA0, polynomialCode_L = 0x01;// 多项式码 0xA001

            for (int i = 0; i < bytes.Length; i++)
            {
                crcRegister_L = (byte)(crcRegister_L ^ bytes[i]);

                for (int j = 0; j < 8; j++)
                {
                    byte tempCRC_H = crcRegister_H;
                    byte tempCRC_L = crcRegister_L;

                    crcRegister_H = (byte)(crcRegister_H >> 1);
                    crcRegister_L = (byte)(crcRegister_L >> 1);
                    // 高位右移前最后 1 位应该是低位右移后的第 1 位：如果高位最后一位为 1 则低位右移后前面补 1
                    if ((tempCRC_H & 0x01) == 0x01)
                    {
                        crcRegister_L = (byte)(crcRegister_L | 0x80);
                    }

                    if ((tempCRC_L & 0x01) == 0x01)
                    {
                        crcRegister_H = (byte)(crcRegister_H ^ polynomialCode_H);
                        crcRegister_L = (byte)(crcRegister_L ^ polynomialCode_L);
                    }
                }
            }

            return new byte[] { crcRegister_L, crcRegister_H };
        }

        /// <summary>
        /// Modbus的CRC16
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static byte[] ModbusCrc16(List<byte> bytes)
        {
            return ModbusCrc16(bytes, 0, bytes.Count);
        }

        /// <summary>
        /// Modbus的CRC16
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static byte[] ModbusCrc16(List<byte> bytes, int offset, int length)
        {
            byte crcRegister_H = 0xFF, crcRegister_L = 0xFF;// 预置一个值为 0xFFFF 的 16 位寄存器

            //byte polynomialCode_H = 0xA0, polynomialCode_L = 0x01;// 多项式码 0xA001

            for (int i = offset; i < offset+length; i++)
            {
                crcRegister_L = (byte)(crcRegister_L ^ bytes[i]);

                for (int j = 0; j < 8; j++)
                {
                    byte tempCRC_H = crcRegister_H;
                    byte tempCRC_L = crcRegister_L;

                    crcRegister_H = (byte)(crcRegister_H >> 1);
                    crcRegister_L = (byte)(crcRegister_L >> 1);
                    // 高位右移前最后 1 位应该是低位右移后的第 1 位：如果高位最后一位为 1 则低位右移后前面补 1
                    if ((tempCRC_H & 0x01) == 0x01)
                    {
                        crcRegister_L = (byte)(crcRegister_L | 0x80);
                    }

                    if ((tempCRC_L & 0x01) == 0x01)
                    {
                        crcRegister_H = (byte)(crcRegister_H ^ polynomialCode_H);
                        crcRegister_L = (byte)(crcRegister_L ^ polynomialCode_L);
                    }
                }
            }

            return new byte[] { crcRegister_L, crcRegister_H };
        }
    }
}
